| From the pages of Pottery Making Illustrated
An Extruded Palette by Jim Robison
Extruded detail elements can add precise control and strong defined edges to handbuilt vessels.
| 
The form of this slab planter is enhanced by a substantial extruded rim.
|
Extrusions have proved to be a breath of fresh air in my studio. Not
just as an alternative to other building methods, but as an added bonus
in the studio schedule. Since Iowa college days in the 60s, my emphasis
has been on a broad church approach to work, with variety and
playfulness seen as an essential part of the making process. Since
ceramics was seen as part of an art curriculum, courses taken in
painting, drawing and sculpture influenced my ceramic work.
Handbuilding
offers extensive possibilities; the clay slab may be treated much as a
painter’s canvas with the additional qualities of high relief texture
and three-dimensional form. Extrusions can provide an element of
precise control, with defined edges and form that also strengthen the
fragile edge of the piece. When my standard building processes become a
bit stale, a new profile for a rim, foot or handle created using the
extruder can make a dramatic change.
 |  | |
Figure 1: A variety of extruder dies for rims. |
Figure 2: Extruded rim with formed groove. |
|
Rims
Rims are one way any vessel comes to a visual close, as all lines lead
upward to the mouth of the piece. The ways to achieve a successful
ending are many of course, but a generous rim or lip is seen by many
potters as a key to a successful pot. I suppose in throwing
terms, the presence of a well-finished, proportional rim means that you
did not have to struggle to raise the cylinder in the first place and
had plenty of clay left over for this final ending curve. Often the
profile of the lip is formed early in the process to make sure that
this is possible, and the final shape is refined afterwards.
Just as with thrown forms, irregular slabs and extruded tubular pots
seem to cry out for a finishing detail that makes the endings visually
proportional to the form and an integral part of the overall design. It
may be smooth and clean or undulating and active, a small line or a
large architectural detail casting a shadow over the entire piece. One
design solution may simply draw a line around the edge while another
might be quite imposing and become a focus in its own right. The choice
is yours and with extrusions, there is the opportunity to determine the
size and weight of the rim as you study individual pieces.
A piece of thin plywood, plastic or metal, a drill (or Dremel), fret
saw and set of files will create a myriad of die shapes (figure 1). I
have begun to incorporate notches into the die shapes I make, creating
an indented groove in the final extrusion that helps it to register
securely over the top edge of the slab (figure 2). The increase in the
surfaces of the pot and the rim that now come into contact means that
the rim is securely attached to the piece with no messy joins to smooth
out.
|
Legs
While attempting to make large bowls and hanging wall plates from
irregular slabs, other problems emerged that I have since solved with
the addition of extruded elements. One recurring problem stemmed from
the fragility of unfired clay. Uneven slabs with holes lack the basic
strength of uniform sheets or thrown bowls (figure 3). My own desire to
raw glaze and exclude the usual bisque firing compounded this problem;
even when spraying thin layers of glaze, the combination of moisture
and handling often meant a sizeable loss rate.
Warping and slumping of stoneware forms during the glaze firing was
another problem I encountered. As the vitrification process fuses and
melts the clay and gravity takes its toll, a form that started out as a
nice, deep, rounded bowl may well look nearly flat by the end of the
firing. Even when the effects of firing are not this extreme, there
usually are cracks and sagging, which distort the original intent of
the work.
Extruded details that began as simple feet for these dishes have now
grown into linear details that cross the entire piece, as I found that
these added elements prevented some of the problems I was experiencing
during the glaze firings. These extruded elements may be profiled to
fit the curved form and incorporate feet for the dish at the same time.
Applied to the leather-hard state while the bowl is inverted over a
hump mold, these strips of clay give considerable strength to the
slabs, acting both as reinforcement to the stressed slab in the green
state and support for the bowl during firing. In some cases, I use
additional props to support the edges during firing. The result has
been a dramatic cut in the overall loss rate during glazing and a
significant reduction in distortion during firing. Other benefits of
attaching extruded strips to the bottom of the forms include the
structured and finished appearance for the under side of the forms and
the creation of a place to attach a wire for a wall-hung work (figure 4).
|
 |  |  |  |
| Figure 3: Dish with extruded ribs for added support. |
Figure 4: Extruded ribs used for reinforcement and as feet. |
Figure 5: Extrusions used to create a tripod vase.
|
Figure 6: Detail showing temporary support for firing a tripod vase. |
Tubes
Recently I began to explore folding textured slabs into more rounded
and irregular shapes to get away from flat bottomed forms. I throw
slabs against my stone and block studio walls, drop them a few times
and wrap them into shape on a foam pad. Clay tubes, curved as they are
extruded, are added as tripod legs for these pieces when they are
leather-hard. The result is a pot that not only escapes from flat sided
rigidity but also has an animated quality (figure 5).
Of course, building like this creates its own set of problems including
support for the work in the making and drying and allowing for movement
of the piece caused by shrinkage during firing (which can cause the
legs to pull away from the body of the pot). The making problems have
now been largely overcome by building the work in an inverted position.
Legs now project up into the air while being attached, free to wave
about and be adjusted for length and angle. A board placed on top helps
me to see the likely level position of the pot when turned the right
way up.
I solved the drying and firing problem by building a central support
for the weight of the pot and attaching it to a slab. This support will
stay under the piece once it is turned right side up to finish drying
and when it is fired (figure 6). After drying, the work is lightly
spray glazed with a matt, raw, clay based glaze. This type of glaze
does not cause the piece to stick to its support and slab. During the
firing, the support structure prevents the piece from slumping, and
acts as a firing slab or kiln waster, shrinking at the same rate as the
pot, absorbing the friction from sliding across the kiln shelf as the
clay shrinks and preventing the feet from breaking off.
All in all, an extruder offers the ability to add variety, with
precision to any body of work. It may even be the work itself of
course, becoming the starting point as well as a finishing off place
for the creative juices. •
Jim Robison has been a potter for more than 40 years. He is the author
of Large-scale Ceramics, co-published by the American Ceramic Society
and A&C Black (London). For more information about Jim and to view
his work, go to www.boothhousegallery.co.uk. |
Subscribe Today to get great content like this delivered right to your door!
|
|